This invention relates to a system for replacing fuel gas in the fuel feed system of a fuel cell with other gas at the time of start and stop of operation of the fuel cell.
It is well known that a fuel cell is made of a cell stack comprising plural single cells each composed of a pair of fuel electrode and oxidizing agent electrode between which an electrolyte is pinch-held. Fuel gas containing hydrogen and oxidizing agent such as air or oxygen are fed to the cell stack to generate electricity. Various fuel cells such as an alkaline type, a phosphoric acid type and a fused carbonate type, etc. are classified in accordance with the kinds of their electrolytes or operating temperatures. At the time of start and stop (including emergency stop) of operation of these fuel cells, the gases in fuel gas feed and discharge systems including the fuel cell bodies are generally replaced with inert gas such as nitrogen gas in order to secure safety. When the fuel cell whose operation has been stopped is put in operation again, detonating gas is likely to be produced and dangerously explode if the fuel gas is fed to the fuel cell having air or oxygen remaining in the fuel system of the fuel cell. When the operation of the fuel cell is stopped, the pressure of fuel gas is likely to decrease due to the internal discharge of the fuel cell, a temperature change of the fuel cell or the like so that air enters into the fuel system to produce detonating gas if the fuel gas is left in the body of the fuel cell. For these reasons, the gas replacement described above is performed in order to secure safety.
In order to perform the gas replacement in a conventional fuel cell equipment, the inert gas is previously stored in a storage tank such as a pressure container separately from the fuel and oxidizing agent feed systems of the fuel cell equipment. At the time of start and stop of operation of the fuel cell, the inert gas is fed from the storage tank to the reacting gas system of the fuel cell. Such a method requires not only the management of fuel but also requires other troublesome managements such as the monitoring of the quantity of the inert gas remaining in the storage tank, the securing of inert gas stockpile and the purchase or acquisition of the inert gas. As for a fuel cell equipment used as a portable power source in particular, a large storage tank for inert gas needs to be provided and conveyed together, which results in enlarging the whole equipment.